Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
172
ISSN 1392–1320 MATERIALS SCIENCE (MEDŽIAGOTYRA). Vol. 24, No. 2. 2018
Comparison of Plasma Transferred Arc and Submerged Arc Welded Abrasive
Wear Resistant Composite Hardfacings
Taavi SIMSON 1 , Priit KULU 1, Andrei SURŽENKOV 1, Antanas CIUPLYS 2,
Mart VILJUS 1, Gintautas ZALDARYS 2
1 Department of Mechanical and Industrial Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn,
Estonia 2 Department of Production Engineering, Kaunas University of Technology, Studentu str. 56, 51424 Kaunas, Lithuania
http://dx.doi.org/10.5755/j01.ms.24.2.19121
Received 26 September 2017; accepted 18 December 2017
Composite hardfacings produced by Plasma Transferred Arc Welding (PTAW) and Submerged Arc Welding (SAW)
possess a good combination of hardness, wear resistance and fracture toughness, thus providing high wear resistance.
Although they cannot substitute and be compared with conventional WC-Co based hardmetals, still they can be used in
many applications where high wear resistance, hardness and toughness are in great demand. In this study two different
hardfacing production technologies PTAW and SAW, were used to produce the hardfacings for abrasive wear conditions.
In both cases hardfacings were welded on the top of low alloy steel using different proportions of disintegrator milled
hardmetal WC-Co powder of different fractions as a reinforcement and self-fluxing alloy as a matrix. They were analysed
in regard to Rockwell and Vickers hardness, wear behaviour, and microstructural analysis. SAW hardfacings were
subjected to Rockwell hardness test after process and after two cycles of tempering; secondary hardness effect was detected
as increment of hardness values from 39 HRC to 58 HRC after first cycle of tempering. High Vickers hardness values did
not correlate with wear results, as it commonly shows hardness of hardmetal particles. Dissolution of hardmetal particles
in the matrix was observed in both PTAW and SAW hardfacings with higher amount in the later. This amount correlated
with heat input during welding process. Wear test results in abrasive emery wear (AEMW) and abrasive wheel wear test
(AWW) showed almost analogous tendency, with slightly lower wear in later. Both types of hardfacings have shown
promising results in intensive wear conditions.
Keywords: hardfacing, plasma transfer arc welding, submerged arc welding, wear resistance, recycled powder.
1. INTRODUCTION
In the majority of wear parts applications there is a great
demand for hard materials with superior wear resistance in
the form of coatings or hardfacings [1]. Hardfacing
procedure can be used for the production of new overlays as
well as for restoration of worn surfaces [2, 3]. Different
types of welding, brazing, powder metallurgy (liquid phase
sintering), laser-cladding, thermal spraying, etc., are widely
used for the production of hardfacings [4].
Among other hardfacing methods, welding is
considered as an economical choice [5]. A solid wire is used
as an electrode to form a hard high wear resistant layer on
the surface of a substrate using different welding processes
such as Gas Tungsten Arc Welding (GTAW), Flux Cored
Arc Welding (FCAW), Gas Metal Arc Welding (GMAW)
or Submerged Arc Welding (SAW). SAW is a fascinating
method for the production of hardfacings because of its high
deposition rates. The SAW hardfacing process may indeed
mean melting a pre-placed highly alloyed powder, which
contains elements such a chromium, carbon, molybdenum,
tungsten, and manganese, by the electric arc under the layer
of flux [6, 7].
Generally, SAW hardfacings are used in abrasion,
erosion, corrosion or impact wear conditions: mineral
processing, mining, cement production, and paper
Corresponding author. Tel.: +372-58-208242.
E-mail address: [email protected] (T. Simson)
manufacturing. Some of specific applications are similar to
those of Plasma Transferred Arc Welded (PTAW)
hardfacings such as crusher teeth, hydro transport screens,
and pumps [8, 9].
In its turn, PTAW is among the favoured production
technologies to produce hardfacings with lower
manufacturing cost and higher productivity compared with
thermal spraying, laser cladding or a similar technology
[10]. The main advantages of these coatings are their density
and high thickness that are necessary for mining, oil-sand
industries, mixer blades, furnace chutes, etc. [11, 12].
PTAW iron-based hardfacings, reinforced with WC-Co
particles, may provide over 9 times higher resistance to
abrasive wear, than commonly used wear resistant steels
[13]. This process normally uses powder mixture carried
into the arc area using powder feeding system [6]. There are
only a few different powder materials systems that are
typical to PTAW and SAW: chromium carbide, WC-Ni and
WC-Co, etc. Because of comparatively high price of PTAW
equipment it is impractical to produce relatively low value
added hardfacings such as chromium carbide overlays,
therefore more expensive materials systems such a WC,
WC-Co, self-fluxing alloys, Fe-Cr-C alloys, stellites, etc.,
are used; on the other hand, SAW technique is seldom used
for production of tungsten carbide based coatings because
of extremely high weld arc temperatures, which can initiate
173
the dissolution of tungsten carbide. Considering process
parameters: hardfacing rate, voltage, and feed rate a direct
dependence was observed between the dissolution rate and
the content of WC [14]. The maximum WC content of 19 %
at dissolution rate of 5 % was only realised with low feed
speed and voltage. In the case of the PTAW process, the WC
content may approach 30 % [15].
Taking into account these considerations the main
objective of presented study is applying two common
welding technologies – PTAW and SAW – to produce
hardfacings, compare and analyse mechanical their
properties, formed microstructures and wear resistance in
intensive abrasive emery wear and abrasive wheel wear
conditions.
2. EXPERIMENTAL
Recycled (disintegrator milled) hardmetal WC-Co
powder, with size of 1.6 – 2.0 mm (coarse fraction) and
0.16 – 0.315 mm (fine fraction) as reinforcement and
commercial iron-based self-fluxing alloy powder with
fraction size of 15 – 53 μm as matrix were used as the
feedstock materials for PTAW. In case of SAW, in addition
to hardmetal and the above-mentioned self-fluxing alloy
powders, a low carbon wire was applied as the consumable.
Composition of hardfacings is presented in Table 1.
Table 1. Composition of hardfacings
No. Powder composition, vol.% Method
C5 50 WC-Co 2 + 50 FeCrSiB 1 PTAW
B1 50 WC-Co 2, 50 LCW4 SAW
B2 25 WC-Co 2 + 25 FeCrSiB1 +
+ 50 LCW 4 SAW
D 25 WC-Co 2 + 25 WC-Co 3 +
+ 50 LCW 4 SAW
1 Iron-based self fluxing alloy 6AB (Höganäs AB):
Cr 13.7 wt.%, Si 2.7 wt.%, B 3.4 wt.%, Ni wt.6.0 %,
C 2.1 wt.%, bal. Fe;
2 Disintegrator milled WC-Co powder (Tallinn University of
Technology); particle size 1.6 – 2.0 mm;
3 Disintegrator milled WC-Co powder (Tallinn University of
Technology); particle size 0.6 – 0.315 mm;
4 LCW – low carbon wire (C < 0.1 wt.%, Si < 0.03 wt.%,
Mn 0.35 – 0.6 wt.%, Cr < 0.15 wt.%, Ni < 0.3 wt.%).
The PTAW hardfacing process was carried out in three
steps. Firstly, the matrix self-fluxing alloy bond layer was
deposited, with the deposition rate of 50 mm3/s and current
of 65 A. Secondly, the hardmetal layer with thickness of ~2
mm was manually placed on that layer. Final step was the
deposition of the third layer of the matrix self-fluxing alloy
with the deposition rate of 40 mm3/s and current of 55 A.
The SAW hardfacing process was performed in a single
pass using standard flux AMS1 (LST EN 10204:2004;
SiO2 38 – 44 wt.%, MnO 38 – 44 wt.%, CaF2 6 – 9 wt.%,
CaO 6.5 wt.%, MgO 2.5 wt.%, Al2O3 5 wt.%,
Fe2O3 2 wt.%, S 0.15 wt.%, P 0.15 wt.%) to shield
and prevent contamination of the welding area. Low carbon
single electrode wire with diameter of 1.2 mm was fed at the
25.2 m/h rate into the welding zone under preliminarily
chosen process parameters: welding current 180 – 200 A,
voltage 22 – 24 V, travel speed – 14.4 m/h [16]. SAW was
carried out with an automatic welding device – torch
MIG/MAG EN 500 78). As substrate material for
production of composite hardfacings structural steel S235
(C 0.17 wt.%, Mn 0.55 – 0.65 wt.%, S ≤ 0.05 wt.%,
P ≤ 0.04wt.%) provided as bars with 10 × 10 mm cross-
section was used. The hardfacing was deposited on
10 × 100 mm samples with hardmetal powder mixture
(~ 2 mm) spread on the surface of substrate under the flux.
Harfacings obtained using SAW were tempered after
welding, at first for 1 h at 550 °C, with following tempering
for 1 h at 600 °C.
Scanning electron microscope (SEM) images of
harfacings were obtained using SEM EVO MA-15 from
Carl-Zeiss.
Rockwell hardness of hardfacings was measured on the
wrought (as welded) and heat treated (tempered) samples
using Universal hardness tester Verzus 750CCD at the load
of 1470 N with diamond indenter. Vickers hardness (9.8 N)
was measured using Buehler Micromet 2001 hardness
tester. An average of 10 for Rockwell and 20 for Vickers
hardness readings are reported in the results.
Two different wear testing methods were used to
evaluate and compare wear resistance of produced
hardfacings: Abrasive Emery Wear Test (AEMW) (Fig. 1)
and Abrasive Wheel Wear (AWW) (Fig. 2). Technological
parameters of wear test methods are given in Table 2.
Fig. 1. Scheme of abrasive emery wear test: 1 – worn samples;
2 – holder; 3 – emery substrate
Table 2. Parameters of wear testing methods
Wear testing methods
AEMW Speed – 0.4 m/s, duration – 60 min, distance –
1440 m, abrasive – electrocorundum/white
aluminium oxide 15A8HM with 8H mesh size
AWW Speed – 2.4 m/s, duration – 10 min,
distance – 1440 m, abrasive – SiC, particle size –
600 – 800 μm; wheel hardness – 35 HRC
Samples for AEMW test (Fig. 1) with dimensions
6 × 20 mm were pressed to the emery substrate with 5 N
load. Wear samples have been rotating round the holder axis
with velocity of 63 r/min. Mass loss has been checked after
each 10 min of test (~ 240 m of wear path) on the scales with
0.0001 g accuracy. Electrocorundum/white aluminium
oxide was used as abrasive emery substrate; it was changed
every 5 min (~ 120 m of wear path).
174
AWW test was carried out by testing machinery
assembled in Tallinn University of Technology. AWW test
(Fig. 2) imitates two-body abrasive wear conditions, in
which test body is pressed against revolving abrasive wheel
with fixed abrasive at speeds that are similar to Abrasive
Rubber Wheel Wear (ARWW) test, carried out according to
ASTM G65 standard.
Each presented hardfacing C5, B1, B2, D was tested
four times, and just the average results of hardness and wear
were analysed and discussed.
Fig. 2. Scheme of abrasive wheel wear: 1 – abrasive wheel;
2 – testbody holder; 3 – weight
3. RESULTS AND DISCUSSION
The purpose of multiple step tempering was to reduce
the stresses and initiate transformation of possibly retained
austenite [7]. After the first tempering at a temperature of
550 ºC, hardness of hardfacings B1 and B2 reached 55 HRC
(Table 3). Further tempering at 600 °C did not affect
hardness values of this testing lot. Different results were
observed for the sample D, produced from the hardmetal
powder of fine and coarse fracture. Fine particles dissolved
completely forming highly alloyed matrix, while coarse
particles remained almost unaffected. Obviously hardness
of sample D as welded was just 39 HRC, though it increased
to 58 HRC and 54 HRC respectively after tempering at
550 °C and 600 °C. This is typical to the so called secondary
hardening of e.g. high speed steels and high alloyed tool
steels. Secondary hardness was caused by the
transformation of retained austenite or by the precipitation
of carbides.
Table 3. Hardness of hardfacings
Rockwell hardness of SAW hardfacings after tempering
No. As welded,
HRC
After tempering, HRC
550 °C (I cycle) 600 °C (II cycle)
B1 55 55 54
B2 54 53 50
D 39 58 54
Vickers hardness, HV1
Matrix C5 B1 B2 D
846 1425 1441 1557 1436
The microstructures hardfacings’ cross-section views
produced using SAW clearly revealed hardmetal particles
with narrow diffusion zones, where iron from matrix
substitues cobalt, (I) tightly distributed into the metal matrix
(II) Between hardmetal particles and matrix there is also
precipitation zone (III), where loose WC are precipitated in
the matrix (Fig. 3, Fig. 4, Fig. 5) [19].
Fig. 3. Microstructures of SAW hardfacing B1: I – diffusion zone
II – metal matrix; III – precipitation zone
Fig. 4. Microstructures of SAW hardfacing B2: I – diffusion zone;
II – metal matrix; III – precipitation zone
Fig. 5. Microstructures of SAW hardfacing D: I – diffusion zone;
II – metal matrix; III – precipitation zone
It is clearly seen in microstructure images of
hardfacings B1, B2 and D (Fig. 3 – Fig. 5) that tungsten
carbide-cobalt powder particles dissolute (II) under the
influence of high SAW weld pool temperature. Such a
dissolution of WC-Co increases hardness of the matrix, but
I
II
III
I
II III
I II
III
175
probably would decrease overall wear resistance of the
hardfacings [6, 16].
The solidification of hardfacings started when primary
carbides were formed, followed by eutectic change of liquid
solution to austenite. The ledeburitic eutectic surrounds the
primary carbides and forms matrix of SAW hardfacings
(dark grey sectors around the WC-Co particles). Low carbon
wire and self-fluxing alloy form a matrix in the coating with
a structure similar to a cast structure (II).
Some relief cracks have appeared almost in all
microsections in the area of hardmetal particles during
mechanical operations of sections preparations: cutting,
grinding and polishing. These cracks have caused just initial
increase of mass loss during wear test.
As can be seen from Fig. 6, during PTAW welding
similar dissolution of hardmetal particles in the matrix takes
place as in SAW (II). Amount of dissolution is in correlation
with heat input during welding process. Former
investigations [17] confirmed this statement: the decreased
content of WC was related to thermally induced degradation
from increased dissolution and increased iron content in the
melt.
Fig. 6. Microstructure of PTAW hardfacing C5: I – diffusion zone;
II – metal matrix; III – precipitation zone
SAW and PTAW produced hardfacings were tested in
two abrasive wear conditions: emery wear (Fig. 7) and
abrasive wheel wear (Fig. 8). Mass loss results were
registered for two wear scars in abrasive emery wear test
and four wear scars in abrasive wheel wear test. Generally,
first wear scar associates with intensive wear, because
heavier WC-Co particles precipitate at the bottom of
coating.
Matrix material is cut out by abrasive particles at the
beginning. At later test abrasive cannot reach matrix no
more, so then it is protected by hardmetal particles.
As can be seen, values of first wear scar tests are quite
high for the both experimental tests: maximum mass loss in
AEMW was 136.4 mg, in AWW test – 126.8 mg (Fig. 7 and
Fig. 8 respectively). After reaching such a high mass loss
for all tested samples, it was decided by grinding operation
to remove approximately the 1.5 mm from the surface of
hardfacings tested on AEMW (2 wear scars), and to carry
out additional wear tests on the hardfacings in the case of
AWW test (4 wear scars).
Fig. 7. Abrasive emery wear test results of hardfacings
Fig. 8. Abrasive wheel wear test results of hardfacings
Obtained results have proved the presumption that
heavy hardmetal particles lay at the bottom – wear
resistance of ground hardfacing B1 has been increased by 6
times: initial mass loss – 86.05 mg, after removal of
superficial layer – 13.2 mg. The same tendency is seen for
hardfacing D – mass loss has been decreased by 6 times too
while for B2 this difference was two times lower (Fig. 7).
PTAW produced hardfacing C5 was less sensitive to the
second wear test after grinding – mass loss values were just
1.6 times lower.
Wear resistance of hardfacings tested on AWW
machinery have been increasing after each 1440 m of wear
path. It was depicted in the previous research [18] that
composite hardfacings containing coarse WC-Co
reinforcement (1.6 – 2.0 mm) suit well for two-body
abrasion condition (AWW). Total length of wear path was
5760 m; as can be seen in Fig. 8, character of wear
behaviour of SAW and PTAW samples in wheel test was
analogous to the emery wear test. Mass loss after second test
for all hardfacings was approximately 2 times lower than
after the first one. The maximum reduction in worn mass
loss was reached after third wear test – for all hardfacings in
average by 9 times. Results of further wear test for B1, B2,
and D hardfacings showed subsequent increase in wear
resistance (on average twice) demonstrating suitability of
produced hardfacings for long-term intensive wear, because
deeper portions of coatings showed gradually increasing
wear resistance.
I
II
III
176
4. CONCLUSIONS
Wear test results in abrasive emery wear and abrasive
wheel wear test showed almost analogous tendency (when
comparing first and second scars), with slightly lower wear
values in AWW compared to AEMW.
PTAW produced hardfacing C5 showed better wear
resistance than SAW hardfacings B1, B2, and D in both
wear test conditions: mass loss of the former was by 5.9 and
2 times lower after first and second wear test respectively in
abrasive emery test, and on average by 3.2 lower in abrasive
wheel test.
Behaviour of SAW hardfacings B1, B2, and D is
promising – third and fourth test series showed very high
wear resistance, indicating that hardfacings need “working
in” before achieving maximum wear resistance.
Secondary hardening effect was observed after two
cycles of tempering of hardfacings produced by submerged
arc welding. It led to the formation of high wear resistant
substrate.
Acknowledgments
This work was supported by institutional research
funding IUT19-29 „Multi-scale structured ceramic-based
composites for extreme applications“ of the Estonian
Ministry of Education and Research.
This work was partially supported by Erasmus+ staff
exchange program by Archimedes Foundation.
REFERENCES
1. Hinners, H., Konyashin, I., Ries, B., Petrzhik, M.,
Levashov, E.A., Park, D., Weirich, T., Mayer, J.,
Mazilkin, A.A. Novel Hardmetals with Nano-Grain
Reinforced Binder for Hard-Facings International
Journal of Refractory Metals and Hard Materials 67
2017: pp. 98 – 104.
https://doi.org/10.1016/j.ijrmhm.2017.05.011
2. Bendikiene, R., Pupelis, E., Kavaliauskiene, L. Effects of
Surface Alloying and Laser Beam Treatment on the
Microstructure and Wear Behaviour of Surfaces Modified
Using Submerged Metal Arc Welding Materials Science
(Medžiagotyra) 22 (1) 2016: pp. 44 – 48.
http://dx.doi.org/10.5755/j01.ms.22.1.7621
3. Bendikiene, R., Ciuplys, A., Kavaliauskiene, L.
Preparation and Wear Behaviour of Steel Turning Tools
Surfaced Using Submerged Arc Welding Technique
Proceedings of the Estonian Academy of Sciences 65 (2)
2016: pp. 117 – 122.
http://dx.doi.org/10.3176/proc.2016.2.01
4. Flores, J.F, Neville, A., Kapur, N., Gnanavelu, A. An
Experimental Study of the Erosion-Corrosion
Behaviour of Plasma Transferred Arc MMCs Wear 267
2009: pp. 213 – 222.
https://doi.org/10.1016/j.wear.2008.11.015
5. 50 Hardfacing Tips. Form no. 9220. Victor Technologies,
2012; available at http://studylib.net/doc/18905505/50-
hardfacing-tips---victor-technologies]
6. Mendez, P.F., Barnes, N., Bell, K., Borle, S.D.,
Gajapathi, S.S., Guest, S.D., Izadi, H., Gol, A.K.,
Wood, G. Welding Processes for Wear Resistant Overlays
Journal of Manufacturing Processes 16 2014: pp. 4 – 25.
https://doi.org/10.1016/j.jmapro.2013.06.011
7. Bendikiene, R., Ciuplys, A., Pupelis, E. Research on
Possibilities to Replace Industrial Wear Plates by Surfaced
Coatings using Waste Materials International
Journal of Surface Science and Engineering 10 (4)
2016: pp. 330 – 338. https://doi.org/10.1504/IJSURFSE.2016.077535
8. Chang, C.M., Chen, L.H., Lin, J.H., Fan, C.M., Wu, W.
Microstructure and Wear Characteristics of Hypereutectic Fe-
Cr-C Cladding with Various Carbon Contents Surface &
Coatings Technology 205 2010: pp. 245 – 250. https://doi.org/10.1016/j.surfcoat.2010.06.021
9. Kirchgaßner, M., Badisch, E., Franek, F. Behaviour of
Iron-based Hardfacing alloys under abrasion and Impact
Wear 265 2008: pp. 772 – 779. https://doi.org/10.1016/j.wear.2008.01.004
10. Rojacz, H., Zikin, A., Mozelt, C., Winkelmann, H.,
Badisch, E. High Temperature Corrosion Studies of Cermet
Particle Reinforced NiCrBSi Hardfacings Surface &
Coatings Technology 222 2013: pp. 90 – 96.
https://doi.org/10.1016/j.surfcoat.2013.02.009
11. Zahiri, R., Sundaramoorthy, R., Lysz, P.,
Subramanian, C. Hardfacing Using Ferro-Alloy Powder
Mixtures by Submerged Arc Welding Surface & Coatings
Technology 260 2014: pp. 220 – 229.
https://doi.org/10.1016/j.surfcoat.2014.08.076
12. Saha, A., Mondal, S.C. Multi-objective Optimization of
Manual Metal Arc Welding Process Parameters for Nano-
structured Hardfacing Material Using Hybrid Approach
Measurement 102 2017: pp. 80 – 89. https://doi.org/10.1016/j.measurement.2017.01.048
13. Kulu, P., Tarbe, R., Žikin, A., Sarjas, H., Surženkov, A.
Abrasive Wear Resistance of Recycled Hardmetal Reinforced
Thick Coating Key Engineering Materials 527
2013: pp. 185 – 190. https://doi.org/10.4028/www.scientific.net/KEM.527.185
14. Günther, K., Liefeith, J., Henckell, P., Ali, Y.,
Bergmann, J.P. Influence of Processing Conditions on the
Degradation Kinetics of Fused Tungsten Carbides in
Hardfacings International Journal of Refractory Metals and
Hard Materials 70 2018: pp. 224 – 331. https://doi.org/10.1016/j.ijrmhm.2017.10.015
15. Surzhenkov, A., Baroninš, J., Viljus, M., Traksmaa, R.,
Kulu, P. Sliding Wear of Composite Stainless Steel
Hardfacing under Room and Elevated Temperature Solid
State Phenomena 267 2017: pp. 195 – 200. https://doi.org/10.4028/www.scientific.net/SSP.267.195
16. Liyanage, T., Fisher, G., Gerlich, A.P. Microstructures and
Abrasive Wear Performance of PTAW Deposited Ni-WC
Overlays Using Different Ni-alloy Chemistries Wear
274 – 275 2012: pp. 345 – 354. https://doi.org/10.1016/j.wear.2011.10.001
17. Choi, L., Wolfe, M., Yarmurch, M., Gerlich, A. Effect of
Welding Parameters on Tungsten Carbide-metal Matrix
Composites Produced by GMAW Proceedings of Canadian Welding Association Conference 2011.
18. Simson, T., Kulu, P., Surženkov, A., Tarbe, R.,
Goljandin, D., Tarraste, M., Viljus, M., Traksmaa, R.
Wear Resistance of Sintered Composite Hardfacings under
Different Abrasive Wear Conditions Materials Science
(Medžiagotyra) 23 (3) 2017: pp. 249 – 253. http://dx.doi.org/10.5755/j01.ms.23.3.16323
19. Simson, T., Kulu, P., Surženkov, A., Goljandin, D.,
Tarbe, R., Tarraste, M., Viljus, M. Optimization of
Structure of Hardmetal Reinforced Iron-Based PM
Hardfacings For Abrasive Wear Conditions Key Engineering
Materials 721 2017: pp. 351 – 355.
https://doi.org/10.4028/www.scientific.net/KEM.721.351